You don't need to dereference the filehandle with *. If you leave it out the code should work:

    #!/usr/bin/perl -w

    use strict;

    open TMP, "> file.tmp" or die "Couldn't open file: $!\n";

    my %hash;

    $hash{tmpfile} = \*TMP;

    print {$hash{tmpfile}} "hello, world\n";
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--
John.